11115 research outputs found
Sort by
Identification of structures within higher dimension Poincaré maps relating to quasi-periodic transforming orbits
No full textTwo-dimensional Poincaré maps are widely used for discovering planar periodic and quasi-periodic orbits. These maps have well-defined and easily identifiable chains of islands that are indicative of quasi-periodic orbits. These chains of islands surround fixed points, which indicate periodic orbits. When expanding the Poincaré maps to four dimensions the problem becomes more complex, not only must the four dimensions be displayed in a manner that can be easily interpreted visually, but the structures within the Poincaré maps that indicate quasi-periodic motion are much more complex. An additional factor making these structures more complex is that spatial orbits can experience short-term, quasi-periodic behavior similar to that experienced by a planar orbit, but these spatial orbits can also undergo long-term, quasi-periodic behavior that causes periodic change in the shape of the orbit. In addition to providing indications of quasi-periodic behavior, the shape of the 4D Poincaré structures can provide insight into the transforming nature of the orbit. This paper uses the “space-plus-color” method for displaying the 4D Poincaré maps. Various structures within a 4D Poincaré map relating to spatial, quasi-periodic orbits in the Earth-Moon, circular restricted three-body problem are identified and analyzed. Trends among the structures are identified so that inferences can be made about the orbit relating to structures that have not yet been documented. Structures that clearly highlight a fixed point are identified, and a multiple-shooter method is used to converge on the periodic orbit. Similar structures are identified within 4D Poincaré maps with different Jacobi constants to demonstrate that these structures are not unique to a particular Jacobi constant
Guidance, Navigation, and Control for Multi-Agent Inspection of an Unknown Space Object
Get PDFOn-orbit inspection is a rapidly growing mission that enables extending the life of aging legacy space systems through refueling, replacing, or upgrading components. For an inspection operation, multiple agents taking observations simultaneously can more quickly map an RSO and assure an inspection is complete regardless of RSO dynamics. A multi-agent guidance, navigation, and control (GNC) scheme must be designed with cooperation in mind to achieve inspection objectives, while leveraging the unique capabilities of a distributed inspection system. This work splits the GNC system into two parts composed of an offline guidance scheme for translational reference trajectory generation and an online navigation and control loop for reference trajectory tracking and constrained attitude control.
The offline guidance scheme centers on the formulation of optimal control problems (OCPs) in two types: continuous control and NMC-based trajectories. The solution of these OCPs is handled either by transcribing via pseudospectral collocation and then solving with an interior point nonlinear program (NLP) solver or by directly formulating as a static NLP. A novel method for evaluating information gain is proposed that incorporates viewing angle and lighting conditions to evaluate the quality of the information that could be gleaned from the images obtained. Online navigation and control are achieved by leveraging real-time capable factor graph methods, LQR reference trajectory tracking control, and APF-based constrained attitude control. The online scheme is demonstrated to provide a reliable method for tracking a reference trajectory while adhering to the attitude requirements of an inspection mission. Several example scenarios are explored to demonstrate the efficacy of this proposed offline-online hybrid approach and the implemented methods
Optofluidic Passive Parity-time-symmetric Systems
No full textThis research introduces a novel methodology of harnessing liquids to facilitate the realization of parity-time (PT)-symmetric optical waveguides on highly integrated microscale platforms. Additionally, we propose a realistic and detailed fabrication process flow, demonstrating the practical feasibility of fabricating our optofluidic system, thereby bridging the gap between theoretical design and actual implementation. Extensive research has been conducted over the past two decades on PT-symmetric systems across various fields, given their potential to foster a new generation of compact, power-efficient sensors and signal processors with enhanced performance. Passive PT-symmetry in optics can be achieved by evanescently coupling two optical waveguides and incorporating an optically lossy material into one of the waveguides. The essential coupling distance between two optical waveguides in air is usually less than 500 nm for near-infrared wavelengths and under 100 nm for ultraviolet wavelengths. This necessitates the construction of the coupling region via expensive and time-consuming electron beam lithography, posing a significant manufacturing challenge for the mass production of PT-symmetric optical systems. We propose a solution to this fabrication challenge by introducing liquids capable of dynamic flow between optical waveguides. This technique allows the attainment of evanescent wave coupling with coupling gap dimensions compatible with standard photolithography processes. Consequently, this paves the way for the cost-effective, rapid and large-scale production of PT-symmetric optofluidic systems, applicable across a wide range of fields
Air Force Institute of Technology Research Report 2022
Get PDFThis report summarizes the research activities of the Air Force Institute of Technology\u27s Graduate School of Engineering and Management, as well as AFIT\u27s research centers. It describes research interests and faculty expertise; list student theses/dissertations; identifies research sponsors and contributions; and outlines the procedure for contacting entities within the Institution
Assessing Compounding Risks of Airfield Flooding
No full textAt Tyndall AFB, an installation that is highly vulnerable to extreme weather, researchers piloted a unique approach that leverages high-resolution hydrologic-hydraulic models to illuminate resilience concerns affecting drainage systems during compounding climate events
Coarse-Gridded Simulation of the Nonlinear Schrödinger Equation with Machine Learning
No full textA numerical method for evolving the nonlinear Schrödinger equation on a coarse spatial grid is developed. This trains a neural network to generate the optimal stencil weights to discretize the second derivative of solutions to the nonlinear Schrödinger equation. The neural network is embedded in a symmetric matrix to control the scheme’s eigenvalues, ensuring stability. The machine-learned method can outperform both its parent finite difference method and a Fourier spectral method. The trained scheme has the same asymptotic operation cost as its parent finite difference method after training. Unlike traditional methods, the performance depends on how close the initial data are to the training set
Testing of an Organic Metal Halide Perovskite for Fast Neutron Detection
Get PDFIn this work, we synthesized and characterized the Methylhydrazinium Lead Trichloride MHyPbCl3(CH3NH2NH2PbCl3) perovskite as a fast neutron detector. The high hydrogen density of MHyPbCl3 enables efficient energy conversion from a fast neutron into a recoiled proton through the 1H(n,n)1H elastic scattering interaction, thereby, allowing for direct charge detection. Through IV characterization and X-Ray excitation, the crystal demonstrated a high resistivity at 4.43E11 ω cm and a good mobility-lifetime product (μτ) of 9.1E-3 cm2/V respectively, under C60/BCP/Cu and Au contact configuration to form an ohmic-ohmic detector. The crystal showed a good sensitivity to X-rays using an x-ray tube. The feasibility of the direct neutron conversion detector is demonstrated using the fast neutron beam at a Research Reactor. Waveforms from a charge-sensitive pre-amplifier showed distinct radiation-induced pulses from the MHyPbCl3 detector in response to the reactor neutron beam. Using a thermal neutron filter and gamma shielding in the beam, we showed that the pulses produced were more likely from neutron interactions, despite the Pb containing MHyPbCl3 is also sensitive to gamma-rays. With those fast neutron pulses, a post-pulse processing code was used to conduct pulse height analysis (PHA) and reconstruct an energy spectrum
Aircraft detection from satellite imagery using synthetic data
No full textExcerpt: This paper explores the advancement of object detection models within the domain of satellite imagery analysis, focusing on the innovative application of synthetically generated datasets to enhance model performance. Motivated by the inherent challenges of manual dataset annotation, such as errors, limited variability, and geographical biases, this study employs synthetic data generation techniques to create a diverse dataset by overlaying 3D models of 31 different aircraft types onto satellite imagery, creating a dataset of 5000 images containing 27,375 aircraft
Wavelength correlation of Fried’s hidden phase
No full textWe study the wavelength correlation of Fried’s hidden phase for use in two-wavelength adaptive optics systems operating in strong scintillation. We find the correlation to be weak implying that there is little benefit to correcting the hidden phase in such systems
